Rapid shifts of gaze can be accomplished either by movement of the eyes alone (eye saccades) or combined movements of eyes and head (eye-head saccades). The customary oculomotor range (COMR) is that region about "central" orbital position within which a subject tends to make gaze changes by eye saccades. Prior studies suggest that COMR may be approximately plus or minus 15 degrees but it has never been studied systematically. COMR is important because: 1) The reason for its existence is unclear; it may reflect limitations in the brain's ability to compensate for the oculomotor plant, and therefore mapping COMR would also map these limitations; 2) COMR reflects the brain's choice between two different methods of accomplishing a given task (i.e., to use an eye- only or an eye-head saccade). This sort of binary selection process is accessible to electrophysiologic techniques but behavioral studies of COMR are a necessary prerequisite. The proposed investigations would determine methods of measuring COMR, describe the kinematics of eye movements made within and beyond COMR, determine whether COMR is plastic, and examine the effects of diseases of brain, orbit, and neck on COMR. These studies will also clarify the effects of such disease processes on visual function. Furthermore, by quantifying eye movements about eccentric orbital positions, these studies will establish the validity and limitations of some common clinical tests of eye movements.